This invention relates to surgical apparatus and procedures in general, and more particularly to surgical apparatus and procedures for determining the relative position of bones during surgery, and still more particularly to surgical apparatus and procedures for determining the distal displacement and lateral offset of a patient""s femur relative to that patient""s ilium during total hip replacement surgery.
Unacceptable leg length inequalities, mis-sized lateral offsets, and joint dislocations are possible adverse outcomes of total hip replacement surgeries. Leg length inequalities and mis-sized lateral offsets (including, particularly, insufficient lateral offsets) can result in a persistent limp for patients who have undergone total hip replacement surgeries. Also, joint dislocations are more likely to occur if the soft tissue tension across the replaced joint is too lax as a result of a shortened limb and/or an insufficient lateral offset.
It is, therefore, generally desirable to maintain the leg length, and the amount of lateral offset, which existed prior to the total hip replacement surgery. Sometimes, however, it may he desirable during total hip replacement surgery to change the leg length, and/or the amount of lateral offset, so as to compensate for deficiencies existing in the hip joint prior to the total hip replacement surgery.
The desired leg length, and the desired lateral offset, are achieved during the total hip replacement surgery by selecting a femoral head prosthesis which has the appropriate neck length and geometry, and/or by varying the amount of bone resection performed on the femur.
To achieve the desired leg length and lateral offset during total hip replacement surgery, the surgeon typically determines the initial (i.e., pre-dislocation) position of the femur relative to the ilium, based on reference points selected on each of these bones. A number of different devices and methods for measuring the position of the femur relative to the ilium are known in the art. These existing devices and methods are generally used in conjunction with one or more reference pins which are inserted into a convenient location in the ilium, e.g., typically a few centimeters above the acetabulum. The position of the patient""s femur is then measured off the aforementioned one or more reference pins, by measuring to an appropriate reference point on the femur, e.g., typically in the area of the greater trochanter. It should be appreciated that the femoral reference point is typically located in the area of the greater trochanter inasmuch as the greater trochanter is not removed during femoral resection, yet is on the upper part of the femur and hence reasonably close to the patient""s ilium so as to facilitate measurement.
By way of example, various devices and methods for measuring the position of the femur relative to the ilium are disclosed in U.S. Pat. Nos. 5,122,145; 5,423,828; 5,435,321; 5,603,717; 5,616,147; 5,700,268; and 5,755,794.
Unfortunately, however, all of the existing devices and methods for measuring the position of the femur relative to the ilium tend to suffer from one or more significant disadvantages. On the one hand, some of the existing devices only measure the longitudinal displacement of the femur, and they do not measure the lateral offset of the femur. On the other hand, in those devices which can measure both the longitudinal displacement and lateral offset of the femur, the devices tend to be relatively bulky and complicated to install and use.
Accordingly, one object of the present invention is to provide an improved apparatus for simultaneously determining the distal displacement and lateral offset of the femur relative to the ilium.
Another object of the present invention is to provide an apparatus for simultaneously determining the distal displacement and lateral offset of the femur relative to the ilium, wherein the apparatus is adapted for easy installation and removal, whereby a major portion of the apparatus can be temporarily removed from the surgical site so as to provide unobstructed access to the surgical site.
And another object of the present invention is to provide an apparatus for simultaneously determining the distal displacement and lateral offset of the femur relative to the ileum, wherein the apparatus is safe and effective for use in total hip replacement surgeries.
Still another object of the present invention is to provide an apparatus for determining the distal displacement and lateral offset of the femur relative to the ileum, wherein the apparatus will reduce the amount of time normally required to determine the distal displacement and lateral offset of the femur relative to the ileum.
Yet another object of the present invention is to provide an apparatus for determining the relative position of bones during surgery, wherein the bones may comprise bones other than the femur and the ileum.
And another object of the present invention is to provide an improved method for measuring the distal displacement and lateral offset of the femur relative to the ilium.
And another object of the present invention is to provide an improved method for determining the relative position of bones during surgery.
These and other objects of the present invention are addressed by the provision and use of a novel measuring gauge for determining the relative position of bones during surgery.
The novel measuring gauge comprises an anchor, preferably made of stainless steel, having a pointed tip for insertion into, and temporary attachment to, the ilium of the patient. A stop is preferably located on the anchor about 1 to 3 centimeters from the pointed tip. The stop prevents excessive penetration of the anchor into the ilium, which might injure internal organs or neurovascular structures.
An adapter slidingly engages the anchor and sits atop the stop. The pointed tip of the anchor is driven into the ilium bone at a convenient location, usually a few centimeters above the acetabulum. The pointed tip can be driven into the bone by impacting the anchor directly, or by impacting the adapter mounted on the anchor.
An outrigger, comprising a shaft which preferably has a pointer at one end, is adjustably connected to the adapter by a releasable locking joint. The outrigger""s pointer preferably projects at a right angle to the longitudinal axis of the outrigger.
In use, after surgical exposure of the hip joint, and prior to the dislocation of the joint for bone resection, a reference mark, preferably one to two millimeters deep, is made at a convenient location on the greater trochanter of the femur using a sharp pointed device such as the tip of a pin. Alternatively, the reference mark can be made with a marking pen or an electrocautery device. The anchor (with or without the adapter mounted thereon) is positioned in the ilium as described above.
Next, the elements of the measuring gauge are arranged so that the outrigger is adjustably connected to the adapter by the releasable locking joint, with the adapter being seated on the anchor. The tip of the pointer can then be positioned in three dimensional space, using the following degrees of freedom of the adapter, locking joint and outrigger: (1) the locking joint, together with the outrigger, is slidable along the longitudinal axis of the adapter; (2) the locking joint and outrigger can also rotate about the longitudinal axis of the adapter and/or about the longitudinal axis of the anchor; (3) the shaft of the outrigger can also telescope in and out of the locking joint; and (4) the outrigger can also rotate around the long axis of its shaft.
Using the aforementioned degrees of freedom, the measuring gauge is manipulated so that the outrigger""s pointer is positioned over the reference mark on the femur. At this stage, the adapter and outrigger are securely locked together, in a fixed relative position, by firmly tightening the locking joint. In this manner, the position of the reference mark on the femur, relative to the anchor installed on the ilium, is clearly established vis-à-vis the elements of the measuring gauge.
Thereafter, the adapter, locking joint and outrigger are slidingly disengaged from the anchor, as a locked unit, so as to provide the surgeon with unobstructed access to the hip joint.
The hip joint is then dislocated for resection of the appropriate amount of femoral bone.
Following initial preparation of the bone bed, a trial prosthesis is installed in the patient""s femur. This initial trial prosthesis is selected by the surgeon, from an assortment of different prostheses, according to the surgeon""s initial estimate of which prosthesis will achieve the desired results.
The hip joint is then reduced so that the surgeon can check for proper alignment of the prosthesis, any leg length discrepancy, proper lateral offset, and the stability of the hip joint from dislocation. More particularly, after the hip joint has been reduced, the surgeon repositions the adapter, locking joint and outrigger, as a locked unit, over the anchor. This permits the surgeon to check for proper distal displacement and lateral offset of the femur relative to the ilium, by observing any displacement of the outrigger""s pointer from the reference mark placed on the femur""s greater trochanter.
In the usual case, i.e., where the original geometry of the patient""s joint was correct and is to be maintained during the total hip replacement surgery, an appropriate prosthesis will be selected so as to ensure that the outrigger""s pointer is substantially aligned with the reference mark placed on the femur""s greater trochanter.
In other cases, however, the geometry of the patient""s joint is to be changed during the total hip replacement surgery, by varying the distal displacement and/or lateral offset of the femur relative to the ilium. In this case, the desired joint correction is achieved by selecting an appropriate femoral prosthesis so as to ensure that the outrigger""s pointer is displaced a desired distance from the reference mark placed on the femur""s greater trochanter.
After the surgeon has noted the position of the outrigger""s pointer relative to the reference mark placed on the femur""s greater trochanter, the adapter, locking joint and outrigger are then removed, again as a locked unit.
The joint is then dislocated once more, the trial prosthesis is removed, and the permanent prosthesis installed. As noted above, the desired amount of distal displacement and lateral offset is achieved by carefully choosing a prosthesis component of the proper size and geometry, and/or by varying, where possible, the amount of bone which is resected.
After the trial prosthesis has been replaced by the permanent prosthesis, the joint is reduced, and a final check of the joint can be made with the measuring gauge.
Prior to wound closure, the measuring gauge, including the anchor fastened to the ilium, is removed from the surgical site.